In the manufacture of many electronic or electrical components such as integrated circuits, there is a need to deposit thin films on substrates. Materials such as aluminum, titanium, tungsten, tantalum, tantalum nitride, cobalt, and silica may be deposited on ceramic, glass or silicon-derived substrates using physical vapor deposition (PVD) processes such as a physical sputtering process. Another method of deposition of solid materials upon a substrate is chemical vapor deposition (CVD), wherein a solid material is deposited from a gaseous phase onto a substrate by means of a chemical reaction. The deposition reaction involved is generally thermal decomposition, chemical oxidation, or chemical reduction. The CVD process can be used to deposit many elements and alloys as well as compounds including oxides, nitrides and carbides. The thin film deposited may be subsequently etched or otherwise fabricated into circuits and/or other electrical components.
In a typical PVD process, such as physical sputtering, a low pressure atmosphere of an ionizable gas such as argon or helium is introduced in a vacuum chamber. The pressure in the vacuum chamber is reduced to about 10.sup.-6 to about 10.sup.-10 Torr, after which argon, for example, is introduced to produce an argon partial pressure from about 0.0001 Torr (0.1 mTorr) to about 0.020 Torr (20 mTorr). Two electrodes, a cathode and an anode, are generally disposed in the vacuum chamber to generate a plasma in the chamber. The cathode is typically made of the material to be deposited or sputtered, and the anode is generally formed by the enclosure (particular walls of the vacuum chamber, or the support member upon which the substrate sits, for example). At times, an auxiliary anode may be used or the article to be coated may serve as the anode. Typically, a high voltage is applied between these two electrodes to strike a plasma in the chamber, and the substrate to be coated is disposed upon a platform positioned opposite the cathode.
The platform upon which the substrate sits during processing is often heated and/or cooled, and heat is transferred between the platform and the substrate, to assist in obtaining the desired film coating upon the substrate. As device geometries shrink, the coating is preferably a thin film which needs to have an even thickness, controlled stress and the desired material morphology, while providing excellent step coverage. To obtain such a thin film coating, it is desirable to maintain the substrate at a uniform temperature within a few degrees Celsius. Preferably, the temperature is near but below the melting point of the material from which the film is being formed. It is very important that the substrate temperature be repeatable each time a given process is carried out. Thus, the heat transfer between the platform and the substrate must be uniform and repeatable.
In a typical CVD process, to facilitate uniformity of deposition coverage of the substrate, the deposition is carried out in a vacuum chamber under a partial vacuum. The pressure in the CVD chamber commonly ranges from about 0.070 Torr (for plasma enhanced CVD) to about 200 Torr (for "high pressure" CVD). As reactive gases are fed into the chamber, they are directed via a pressure differential (created by the vacuum system applied to the CVD chamber) across the surface of the substrate to be coated in a manner which provides an even flow of reactant gases over the substrate surface. The deposition is also controlled by the temperature of the surfaces which contact the reactant gases. Thus, it is critical that the substrate surface be controlled at a desired uniform temperature.
The substrate support member upon which the substrate sits is commonly used as the means for transferring heat to and from the substrate. Radiant, inductive, or resistance heating are the most commonly used techniques to heat a support platform, but it is also possible to circulate a heat transfer fluid internal to the support platform to provide heating or cooling of the support platform.
When the pressure in the process chamber is about 5 Torr or less, convective/conductive heat transfer between the substrate and the platform becomes impractical. Since the substrate and the platform typically do not have perfectly level surfaces which would enable sufficiently even heat transfer by direct conduction, it is helpful to provide a heat transfer fluid between the platform and the substrate, to assist in providing even heat transfer between the support platform and the substrate. Preferably the heat transfer fluid used between the substrate and its support platform is in constant movement (flowing) to provide yet another improvement in the uniformity of the heat transfer. The heat transfer fluid commonly used between the support platform and the substrate is one of the gases used in the sputtering, CVD or etch process.
A frequently-used substrate support platform design is one having a substrate contact surface which is principally flat-faced with openings and/or exposed channels spaced at various locations upon this surface. The fluid used to transfer heat between the platform and the substrate flows through the openings or is fed through an opening into exposed channels in the flat-faced surface of the platform. The heat transfer fluid can be provided to the platform from a fluid supply source via tubing which connects the fluid supply source to the platform. The platform itself may include various means for directing fluid to the openings and/or exposed channels in the surface of the platform.
In operation of a semiconductor processing apparatus, the substrate to be processed is typically mechanically or electrostatically clamped along its edges to the substrate-facing surface of the support platform. The fluid used to transfer heat between the support platform and the substrate is typically a gas such as helium, argon, hydrogen, carbon tetrafluoride, or hexafluoroethane, for example, or other suitable gas that is a good heat conductor at low pressure. This heat transfer fluid is applied through openings or supplied into exposed channels in the substrate-facing surface of the support platform.
Electrostatic clamping of semiconductor substrates on a support platform, such as a pedestal, is typically accomplished with an electrostatic chuck. An electrostatic chuck typically includes at least a dielectric layer and an electrode, which may be located on a chamber pedestal or formed as an integral part of the chamber pedestal. A semiconductor substrate is placed in contact with the dielectric layer, and a direct current voltage is placed on the electrode to create the electrostatic attractive force to adhere the substrate on the chuck. An electrostatic chuck is particularly useful in vacuum processing environments where the maximum differential pressure which can be established between the low pressure chamber and the face of the chuck is insufficient to firmly grip the substrate on the chuck, or where mechanical clamping of the substrate is undesirable.
Although a simple electrostatic chuck may be formed from as little as a single dielectric layer and an electrode, the materials and construction of an electrostatic chuck will vary from one application to another, particularly in high temperature or low temperature processes. A typical low temperature electrostatic chuck is configured as a thin laminate member supported on a chamber pedestal to receive and support the substrate. The laminate member preferably includes an electrode core, preferably a thin copper member, which is sandwiched between upper and lower dielectric layers of an organic material such as polyamide. An adhesive such as polyamide may be used to attach the polyamide layers to the electrode core. The lower dielectric layer of the laminate member is attached directly to the upper surface of the chamber pedestal, usually with an adhesive such as polyamide, and the upper dielectric layer forms a planar surface on which the substrate is received. To prevent exposure of the electrode to the chamber environment, the upper and lower dielectric layers and adhesive layers extend beyond the edges of the electrode core, and are interconnected at that location to form a dielectric barrier between the electrode core and the chamber environment. To supply the high voltage potential to the electrode, a strap, formed as an integral extension of the laminate member, extends through or around the edge of the pedestal and connects to a high voltage connector on the underside of the pedestal.
Low temperature electrostatic chucks used in certain physical vapor deposition processes are made of a dielectric coated aluminum shell. In both high and low temperature electrostatic chucks, the aluminum shell will typically enclose equipment such as a thermocouple, electrical conductor leads to the electrostatic chuck and a heat transfer gas supply line. When a heating element is included in the shell, the heater must be configured to avoid interference with the other equipment. Unfortunately, the necessary heater configurations do not provide uniform heating of the substrate support platform and, ultimately, the substrate. Temperature nonuniformity of the substrate leads to nonuniform film deposition.
Therefore, there remains a need for a substrate support member that can provide substantially uniform heating over the surface of a substrate and allow for equipment, sensors, wires or the like to pass through or be positioned within the support member. It would be desirable to have a substrate support member with an integral electrostatic chuck in an intimate thermal relationship with a heater. Furthermore, it would be desirable to have a heater that would provide substantially uniform and repeatable heating of a substrate surface.